Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
In one prior art design, the inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
One prior art print cartridge is disclosed in U.S. Pat. No. 4,500,895 to Buck et al., entitled "Disposable Inkjet Head," issued Feb. 19, 1985 and assigned to the present assignee.
The prior art inkjet print cartridges include a number of drawbacks: (1) the metal orifice plate is expensive, difficult to form, and subject to corrosion; (2) the metal orifice plate is difficult to align with the heaters on the substrate and is difficult to affix to the substrate using conventional techniques; (3) the supply of ink to the vaporization chambers is sometimes routed through a center slot formed in the substrate itself, causing added manufacturing complexity and cost and increasing the size of the substrate; and (4) the ink seal between the back of the substrate and a print cartridge body is time-consuming to form.